The present invention relates to techniques for drilling oil, gas, water and geothermal wells or the like. More precisely, the invention relates to cementing compositions and their application to cementing operations known as squeezing operations in such wells.
Cementing operations known as squeezing operations are intended to remedy sealing faults due to cracks, micro-fissures or other cavities in the cemented annulus, the casing or at the cement/casing or formation/casing interface. Such faults are due, for example, to poor positioning of the cement during primary cementing or to holes or fissures which have been deliberately formed, for example at the beginning of the well""s service life, but become redundant as well exploitation progresses.
French patent FR-A-2 735 465 discloses cementing compositions which are particularly suitable for such squeeze cementing operations. In a more particularly preferred variation, such compositions are constituted by:
a base fluid, in particular an aqueous phase;
a dispersing agent in solution in the aqueous phase and optional other liquid additives which are known in the art, in particular anti-foaming agents and retarders or, more exceptionally, cement-setting accelerators;
a cement known as a micro-cement, i.e., a cement constituted by micronic particles;
a first additive constituted by particles 5 to 100 times, preferably of the order of 10 times smaller than the micro-cement particles. Thus the typical average dimension of the particles is in the range 0.05 micrometers (xcexcm) to 0.5 xcexcm such as a latex, a fumed silica type silica condensate, a condensate of manganese oxides in fumed pigments, certain fine soots, carbon black or certain polymer microgels such as a fluid loss control agent;
a second additive constituted by particles 5 to 100 times, preferably of the order of 10 times smaller than the particles of the first additive, such as dispersed colloidal silicas or aluminas (average size 3 nanometers (nm)-60 nm, preferably 15 nm-40 nm), or nanolatexes.
The preferred compositions known from FR-A-2 735 465 advantageously comprise 10% to 40% of the first additive and 5% to 30% of xe2x80x9cultra-finexe2x80x9d particles, the percentages being indicated with respect to the total volume of solid particles in the composition. Compositions comprising 50% to 75% of micro-cement, 15% to 40% of xe2x80x9cvery finexe2x80x9d particles and 5% to 20% of xe2x80x9cultra-finexe2x80x9d particles are more particularly preferred.
The above French patent has also emphasized the necessity for very low fluid losses and a low rheology. In practice, the best penetrations are obtained when such properties are kept under very close scrutiny, aiming for fluid losses of less than 20 ml, a plastic viscosity of less than 60 mPa.s and a yield point in the range 0 to 3 MPa. Such a low rheology is critical for good penetration into the cracks or fissures to be plugged and thus must be measured at the temperature of the slurry in the well. Further, it is also important for the rheology to be low at room temperature to facilitate slurry preparation and pumping.
It has now been discovered that the known compositions described in FR-A-2 735 465 are completely satisfactory at low temperatures but cannot be used when the temperature is raised above 60xc2x0 C. since the plastic viscosity becomes far too high.
The present invention aims to provide novel compositions for squeeze cements, in particular for cementing operations in oil, gas, water and geothermal wells or the like, which have a good ability to penetrate into fissures and which can be used at any temperature which is normal in an oil well, namely between 4xc2x0 C. and 160xc2x0 C. or even 180xc2x0 C.
This aim is achieved by cementing compositions which comprise an aqueous phase, a micro-cement, and an additive essentially constituted by an aqueous suspension comprising:
a three-dimensional vinyl alcohol type polymer obtained by chemically cross-linking, in a reaction with controlled stirring, a polyvinyl alcohol (PVA) in solution with bi-or polyfunctional cross-linking agents which cross-link the alcohol groups (primary, secondary or tertiary), the molar concentration of said cross-linking agent with respect to the PVA monomer residues being in the range 0.1% to 0.5%;
a nanolatex;
an anionic surfactant with a cloud point of more than 80xc2x0 C.
In a more particularly preferred variation of the invention, the weight ratio between the quantities of cross-linked polyvinyl alcohol and nanolatex is in the range 4% to 12%, preferably in the range 6% to 10%, more preferably close to 8%.
The nanolatex used is preferably that disclosed in European patent EP-A-0 644 205 in the name of Rhxc3x4ne-Poulenc Specialty Chemicals and comprising:
93 parts of methyl methacrylate;
5 parts of methacrylic acid;
2 parts of ethylene glycol dimethyl methacrylate.
The quantity of bifunctional monomer can be in the range 0.5 to 6 parts, to obtain a higher degree of cross-linking and thus a glass transition temperature (Tg) of 80xc2x0 C. or more, preferably 100xc2x0 C. or more.
The quantity of monomer comprising a carboxylic function must not exceed the proportions indicated above by too great an extent to prevent the polymer from having a retarding effect on setting of the cement.
The surfactant used in the formulations of the invention is an anionic surfactant. It can be a phosphate-containing, a sulfate-containing or a sulfone-containing surfactant. Sulfate-containing surfactants are preferred. It comprises alkoxylated moieties (preferably ethoxylated). By way of illustration, the number of alkoxylated moieties is in the range 1 to 30.
Sulfated ethoxylated alkylphenol type surfactants, sulfated ethoxylated fatty alcohol type surfactants, and ethoxylated alkylaryl phenol type surfactants are suitable, the latter being more particularly preferred.
It should be noted that the surfactant can also comprise a mixture of alkoxylated (preferably ethoxylated) alcohols. They are compounds which act as wetting and dispersing agents which are compatible with the cement.
The quantity of surfactant, (possibly accompanied by the alcohols cited above) is preferably in the range 3% to 6% (with respect to the total composition).
The additive of the invention is preferably supplied directly in the form of a liquid solution which facilitates its use. In a less preferred variation of the invention, the different additives are added to the aqueous base to form the mixing water to which the micro-cement is added.
The compositions of the invention have extremely low fluid losses, below 15 ml (for a 30 minute test) and a low rheology, with a plastic viscosity of less than 60 mPa.s and a yield point in the range 0 to 2.4 Pa.
The following examples illustrate the invention and furnish advantageous details and characteristics thereof, without limiting its scope. The rheological measurements were carried out after 20 minutes conditioning at the temperature of the measurement, using a Chan 35 rotary viscometer with an outer rotating cylinder, in accordance with API standards, Specification 10, Appendix H. The other measurements were also carried out at the same temperature. The fluid loss tests were carried out using filter paper above the standard screen in accordance with the API standard in the case of the micro-cements.